1. Field of the Invention
The present invention relates to an extender for a universal serial bus (USB) that effectively extends USB cable length above its current approximate five meter limit. Specifically, the invention relates to USB transmit and receive hubs which respectively include non-USB data transport interfaces together with suitable USB-to-non-USB translators, that effectively extend the reach of USB devices.
2. Description of the Related Art
In the evolution of personal computers, one significant recent development is the introduction of universal serial bus (USB). USB is an interface that supports serial data transfers between a USB host computer (sometimes referred to as the xe2x80x9croot nodexe2x80x9d or xe2x80x9croot hubxe2x80x9d) and USB-capable peripherals. The host serves as the master of the bus, and the peripherals perform as slaves connected either directly to the host or indirectly through hubs, in a tiered star topology with one of the hubs at the center of each star.
Without USB, a personal computer requires a separate interface, with specialized electrical, mechanical and software connections, so as to be able to connect to each individual peripheral. Thus, without USB, a personal computer requires separate interfaces for its keyboard, monitor, modem, printer, microphone, joy stick, mouse, scanner, and so forth. With USB, on the other hand, USB-capable peripherals can be connected directly to USB hubs on the bus, without the need for any specialized software interfaces or mechanical or electrical interfaces.
USB is described with specificity in xe2x80x9cUniversal Serial Bus Specificationxe2x80x9d, Version 1.1, Sep. 23, 1998, Compaq Computer Corporation, et al., the contents of which are incorporated herein by reference. Generally speaking, on any USB system, there is exactly one USB host which is typically a personal computer built around USB-capable motherboards and equipped with USB software. The host acts as master of the bus, acknowledging attachment and removal of peripherals, initiating enumeration processes and all subsequent USB transactions on the bus, collecting status and activity statistics, and controlling electrical interface between the host and USB peripherals. USB peripherals act as slaves on the bus and are of two types: xe2x80x9chubsxe2x80x9d and xe2x80x9cfunctionsxe2x80x9d. A xe2x80x9chubxe2x80x9d typically consists of a hub controller and a repeater, and usually converts a single upstream attachment point into multiple downstream attachment ports. xe2x80x9cFunctionsxe2x80x9d are PC peripherals like keyboards, joy sticks, cameras, printers and the like. A xe2x80x9cFunctionxe2x80x9d can be self-powered or bus-powered, meaning it derives its power from the USB bus; likewise, a xe2x80x9chubxe2x80x9d can be self-powered or bus-powered, to provide power to downstream devices (which may be hubs or functions) attached to its ports.
USB cabling, which connects the host with peripherals (i.e., both hubs and functions) consists of four wires including a twisted pair for D+ and Dxe2x88x92 wire and a ground wire. The cabling includes connectors that differ at the upstream and downstream sides, so as to prevent non-USB compliant connections and so as to ease use by preventing mis-cabling: a USB xe2x80x9cAxe2x80x9d type plug on the upstream side toward the USB host, and a USB xe2x80x9cBxe2x80x9d type plug toward the downstream side (towards the peripherals).
While USB provides good interconnectivity between the host and its peripherals, a limitation on the length of USB cabling presents a practical limitation on long distance data transfer. Specifically, because of electrical and frequency constraints, USB cable can be no longer than approximately five meters in length. It is possible to circumvent this length limitation to some extent, by end-to-end connection of multiple USB hubs, each of which acts as a repeater, with separate five meter lengths of cable therebetween. There are other practical limitations on such an arrangement, which in any event is expensive and inconvenient. Accordingly, a better solution is needed.
It is an object of the invention to provide for cable length extension of USB, through the provision of a transmitter hub coupled to a receiver hub over a non-USB data transport connection.
Specifically, according to one aspect, the invention is a USB transmitter hub which includes a USB xe2x80x9cBxe2x80x9d connector for downstream connection to a USB cable. The transmitter hub includes a USB-to-non-USB translator which translates USB communications into a suitable high speed non-USB format, which can be carried over long distances. Preferably, a serial data transport format is preferred, such as a data transport format that can be carried over standard Category 5 cabling over long distances. The transmitter hub further includes a non-USB interface connector, which preferably is an RJ45 connector, for connection over the non-USB data transport connection to the receiving hub.
The non-USB connection between the transmitter hub and the receiver hub can be any suitable high speed and inexpensive interface, including physical connection over copper wire such as the aforementioned category 5 cabling, fiber optic connection, or infrared connection.
The receiver hub includes a complementary non-USB connector, and a complementary non-USB-to-USB translator, all for converting non-USB data transport from the transmitter hub into standard USB protocol. The receiver hub further includes at least one, and preferably several, USB xe2x80x9cAxe2x80x9d connectors for receiving connections from downstream peripherals.
Because a non-USB data transport connection is used between the transmitter hub and the receiver hub, the effective cable length of USB transmissions is limited only by the cable length of the selected non-USB interface, and possibly by timing considerations of the non-USB data transport protocol. For serial data transmission using differential pairs over category 5 cabling, it is possible to extend the effective length to hundreds of feet. Moreover, category 5 cabling is ubiquitous, in that it is typically selected for wiring of local area networks. Accordingly, for installations with existing local area networks, it is possible to use existing cabling, thereby allowing extension of USB capabilities with virtually no installation overhead.
In related aspects, particularly useful where the non-USB connector matches pre-existing connectors, such as the aforementioned RJ45 connector, both the transmitter hub and the receiver hub are equipped with specialized electronics that prevent damage if the transmitter hub or the receiver hub is connected to an inappropriate connection. For example, in an installation with a pre-existing local area network using category 5 cabling with RJ45 connectors, the specialized electronics prevent damage to the transmitter hub and the receiver hub it those hubs were accidentally connected to the local area network; and likewise the electronics prevent damage to the local area network through accidental connection of the transmitter hub or the receiver hub.
This brief summary has been provided so the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of the preferred embodiment thereof in connection with the attached drawings.